Roof challenge

DESIGN A ROOF

OBJECTIVE: To design a car roof with roof essential components by using the master section to design the front roof rail, bow roofs rear roof rails ditch area

2.To determine the heat distortion criteria and snow load criteria and sectional modulus of the roof rails

Roof

An automobile roof or car top is the portion of an automobile that sits above the passenger compartment, protecting the vehicle occupants from sun, wind, rain, and other external elements. Because the earliest automobiles were designed in an era of early automobile roofs used similar materials and designs.

It consists of Front, Rear, Centre, Bow Roof I & II roof rails. Bow roof rails are provided for the support of the roof surface. The bow roofs are provided with mastic sealant as they are assembled with the surface as welding is not possible, whereas the ditch area, front, and rear area is welded with the roof

Front roof rail

Rear roof rail

Bow roof 1

Bow roof 2

Roof thicken

thicken the roof and all bows roof rails with 0.75

All roofs

Cross-sectional view of the roof

Ditch area

Analysis

a. heat distortion criteria

It is the temperature at which the material starts softening when exposed to a fixed load at elevated temperature. Above this temperature, the material can’t be used. In order to know whether the material is in a safer zone according to the positioning of bow roofs, the test is performed by considering the below-given formula

W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8) x (R^2)/t] + [ 1.10x10^(-3) x l] - 2.68

Judgement Condition : OK< 2.7> 3.1

Where

L = Roof Length in X-Direction[mm](Roof dimension in 0-Y)

R = Roof curvature

R = 2(Rx*Ry)/(Rx+Ry)

Rx = X curvature

Ry = Y curvature

t = Roof plate thickness [mm

l = Bow Roof Span [mm]

no	Rx	Ry	R	I	L	t	(R^2)/t	W	OK\NG
BOW1 TOBOW2	3977.71	10579.9	9822.6	504.2	2031.4	0.75	1286446	2.78	ok
BOW2TOREAR ROOF	3274.2	1462.71	4388.1	332.4	2031.4	0.75	2567389	1.15	ok

Judgement Condition : OK< 2.7> 3.1

b. snow load criteria

Snow load Prediction formula

Qr = [Iy x t²] / [α x s x [(Rx + Ry)/2]² x 10^-8]

Note: The Qr value given over here is correct. There was a typo error in the formula given in the video.

Where

α = My x Lx2 x 10-12 , My = Y(Ly-Y)

Judgement condition = Qr ≥ 3.1

250 ≤ s ≤ 380

t = Roof plate thickness [mm]

Ly = Distance between the front and rear roof Rails on the Vehicle along with 0Y[mm]

Length of Roof panel with the center point between Roof rail Front /Rear as the reference point of the front and the rear.

Lx = Distance between the Left and Right end of the roof on the Roof BOW [mm]

Width of the roof panel exposed on the surface.

Y = Distance front Front Roof Rail to Roof BOW[mm]

s = Distance for which Roof BOW bears divided load [mm]

s = L1/2 + L2/2

Iy = Geometrical moment of inertia of Roof BOW (Y cross-section )[mm4]

Rx = Lateral direction curvature radius of roof panel Y cross-section on Roof BOW [mm]

Roof panel curvature Radius of the Length Lx in Front view

Ry = Longitudinal Direction curvature radius of the Roof panel X cross-section on Roof BOW [mm] Roof panel X curvature radius of length s in Side view

S.NO	Iy	t	s	Ly	Lx	Ry	Rx	α	QR	OK\NG
BOW1 TO, BOW2	376.66	0.75	488.5	2031.4	1040.14	11284.3	4289.74	0.832	7.12	OK
BOW2TO, REAR ROOF	506.58	0.75	445.7	2031.4	1039.5	16970.8	3901.7	0.610	5.96	OK

Section modulus study

Front roof rail

Bow roof 1

Bow roof 2

Rear roof rail

conclusion: the roof and ditch area is successfully designed along with heat distortion and snow load test all criteria has passed